Many relatively large gas turbine engines, including turbofan jet engines, may use an air turbine starter (ATS) to initiate turbine engine rotation. The ATS may be mounted by the engine, much as a starter for an automobile is located by the automobile engine. The ATS may be coupled to a high pressure fluid source, such as compressed air, which impinges upon a turbine in the ATS causing it to rotate at a relatively high rate of speed. The ATS includes an output shaft that is coupled to the turbine and, via one or more gears, to the gas turbine engine. The output shaft thus rotates with the turbine. This rotation in turn causes the gas turbine engine to begin rotating.
The flow of compressed air to an ATS may be controlled by, for example, a valve. This valve, if included, is typically referred to as a starter air valve (SAV), and may be controllably moved between a closed position and an open position via a signal supplied from an engine control, such as a full-authority digital engine control (FADEC). When the starter air valve is in the open position, compressed air may flow through the starter air valve, and into the ATS. Conversely, when the starter valve is in the closed position, compressed air flow to the ATS may be prevented. Uncontrolled air flow to the ATS may result in damage to either the ATS or engine gearbox.
Many ATSs presently sense SAV position using a position indication switch or pressure transducer. Both of these types of devices provide either a SAV “closed” indication or a “not closed” indication. These types of devices exhibit certain drawbacks. For example, position indication switches can exhibit relatively low reliability, and pressure transducers, while relatively reliable, are relatively high in cost. Reliable position indication is desirable to prevent damage to the ATS or engine gearbox.
Hence, there is a need for a device that can sense SAV position that both exhibits relatively high reliability and a relatively low cost. The present invention addresses at least this need.